The rate is actually only about 5% higher than the general population. Much lower than average for males in their 20's. Of course, few have as much incentive to behave as these guys, but for the most part they are just average people who happen to be good at sports.
It's hard to get into numbers because there are many instances where an NFL player can sweep their troubles under the rug or avoid prosecution. Steve working at McDonald's will get arrested for punching a coworker. Steve working at Bank of America stadium pays a fine and misses a couple checks.